1. Fields of the Invention
This invention relates to a method and apparatus for the manufacture of shaped articles of polyurethane foam. More particularly, this invention relates to a method and apparatus for manufacturing shaped articles of polyurethane foam with higher safety and lower energy consumption.
2. Description of Prior Arts
The polyurethane foam weighs light and excels in cushioning property of flexibility. Owing to these merits, it has heretofore found extensive utility as cushioning materials in seat cushions for vehicles such as automobiles, railroad coaches and airplanes, in seat cushions for furniture such as chairs, sofas and beds, and in cushions for head rests and arm rests of automobiles. These cushions have been obtained by feeding foamable urethane resin reaction mixture to relevant metal molds and retaining these metal molds for prescribed lengths of time in heating furnaces such as hot blast stoves, electric stoves, or infrared ray stoves maintained at prescribed temperatures thereby foaming and setting the polyurethane dopes within the metal molds. In a plant engaging in the production of cushions for automobile seats, for example, the polyurethane foam cushions are required to possess different hardness and flexibility depending on the types of automobiles and the parts of seats (as between seats and back rests in chairs, for example) in which they are to be used. To satisfy the widely varying needs, therefore, the urethane reaction mixture and the molding conditions are inevitably varied with the types of automobiles and those of seats. In case where one and the same heating furnace is used for the manufacture of cushions of varying requirements, for example, the whole production cycle has to be determined on the basis of the worst of all the molding conditions involved at all.
Unfortunately, the heating furnaces of the class under consideration have a disadvantage that the temperature control is difficult, the maintenance of a constant temperature-elevation curve is difficult, the time for temperature elevation is long, and the temperature distribution is not uniform.
Provision of as many heating furnaces as the varying sets of molding conditions may be one possible solution for the difficulties. The provision of so many heating furnaces entails a huge increase of equipment cost. To overcome these drawbacks, there has been proposed a method which effects the foaming and setting of shaped articles of polyurethane foam in one heating furnace. Since this heating furnace has a small specific heat of air, it suffers from generally inferior thermal efficiency. Moreover, when several types of cushions involving different heating temperatures, heating periods, and foam-setting periods are produced by use of one and the same heating furnace, the operating conditions must be adjusted to the highest of all the foam-setting temperatures and the longest of all the foam-setting times involved. When many types of shaped articles are to be heated at once in the furnace therefore, they invariably undergo the treatment at the highest temperature for the longest period. This means that some of these types of shaped articles have to be treated at a temperature higher than and for a period longer than actually required. This method, therefore, has a disadvantage that the loss of energy amounts to a huge sum.
Further in the production of one type of shaped articles of polyurethane foam, when the aforementioned heating furnace such as, for example, a hot blast stove, an electric stove, or an infrared ray stove is used, there ensues a disadvantage that because air is used as a heat transfer medium, the thermal conduction ratio is low and the threat of fire persists, and because the working temperature is high, the energy consumption is large and the durability of molding metal dies is low.
An object of this invention, therefore, is to provide a novel method and apparatus for the manufacture of shaped articles of polyurethane foam.
Another object of this invention is to provide a method and apparatus for manufacturing shaped articles of polyurethane foam with higher safety and lower energy consumption.
A further object of this invention is to provide a method and apparatus for simultaneous manufacture of varying types of shaped articles of polyurethane foam requiring different molding conditions.